Battery management of lithium ion battery packs for full hybrid, plug-in hybrid, and battery source vehicles using present systems typically uses a battery controller that monitors and balances each cell of the battery. This is very expensive and not consistent with the patterns of cost reduction utilized with other battery chemistries, such as nickel metal hydride (NiMH) batteries. As the control of prior chemistries progressed by development of control electronics monitoring multiple cells, it was possible to monitor every 8, every 10, every 12, or more cells. This has likely not been applied to batteries with lithium cells due to the relative intolerance to overcharges, and has generally demanded individual cell monitoring and control by the battery controller.
However, as the number of cells increases to meet larger battery energy requirements, the monitoring of individual cells, and the corresponding volume of outputs to the battery monitor IC's becomes too complex to practically, efficiently, and inexpensively incorporate in mass vehicle production. With a master controller coupled to dedicated monitoring IC's by serial peripheral interfaces (SPI) when lithium ion batteries may be selected to provide a high energy cell output, even slight overcharges in cell voltages generate cell changes that are very destructive to the cell structure and reduce battery life. Accordingly, attempts to use lithium-ion battery chemistry in mass production electrical vehicles has increased the difficulty of battery management.